Process for the enhancement of power plant with co2 capture and system for realization of the process

ABSTRACT

Improved methods and systems for power plants with CO2 capture and especially power plants with CO2 capture for enhanced oil recovery (EOR) purposes.

FIELD OF THE INVENTION

The present invention generally concerns power plants with CO₂ capture and especially power plants with CO₂ capture for enhanced oil recovery (EOR) purposes.

BACKGROUND OF THE INVENTION

It is known that power plants for the generation of electrical and thermal energy having gas and/or steam turbines driven by fossil fuels may be equipped with systems based on chemical solvent processes (amines, chilled ammonia and others) for the capture of carbon dioxide (CO₂) from the flue gas resulting from the combustion of the fossil fuels; the so called “post combustion carbon capture process”.

It is also known that exhaust gas recirculation can be used in fossil-fired power plants to control the production of gaseous emissions, in particular to enrich the CO₂ content of the exhaust gas, reducing or eliminating the need for costly CO₂ capture.

It is also known that an alternative technology is the so called “oxyfuel process” based on combustion of fossil fuels in an oxygen-enriched stream instead of the ambient air (which contains approximately 21% by volume of oxygen only). If nitrogen is removed prior to combustion, the flue gas stream would then have less nitrogen and the concentration of CO₂ becomes higher, reducing or eliminating the need for costly CO₂ capture.

Following any necessary post-treatment, the separated CO₂ can be forwarded into storage or used for enhanced oil recovery or other purposes.

Further information concerning this technical background can be found in “Developments and innovations in carbon dioxide (CO₂) capture and storage technology”; Volume 1; Carbon dioxide (CO₂) capture, transport and industrial applications; edited by M. Mercedes Maroto-Valer; Woodhead Publishing Limited, 2010, ISBN 978-1-84569-533-0.

In the post-combustion CO₂ capture system the whole flue gas flow is processed at low pressure, therefore this system (apparatus, pipelines, etc.) becomes voluminous and expensive. Some vessels can become so large, that the system is not feasible as a one-train solution, therefore several trains working in parallel are required for realization of such a process.

One issue with the post-combustion CO₂ capture system results from the low CO₂ concentration in the flue gas (3-15% depending on the fuel and combustion system). The efficiency of the chemical solvent process plant depends on the CO₂ concentration in the flue gas, a low CO₂ concentration generally resulting in a low efficiency.

The oxyfuel-based system has a similar problem, i.e. a large amount of air is required to be treated in the air separation unit for the production of the oxygen that goes into combustion. The system therefore becomes large, possibly requiring a multi-train solution and inefficient.

Exhaust gas recirculation has the problem that the oxygen lean recirculation gas, when mixed with incoming ambient air results in a oxygen depleted/CO₂ enriched air stream for the power plant that can affect the output, efficiency, stability and operation of the power plant.

For all of the above reasons, there remains a need in the art for improvements to CO₂ capture from a power plant.

SUMMARY OF THE PRESENT INVENTION

The present invention provides improved techniques for CO₂ capture from a power plant and reuse thereof that is an improvement over the techniques known in the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing showing a fossil fuel power plant with CO₂ capture according to the invention.

FIG. 2 is a schematic drawing showing a fossil fuel fired combined cycle power plant with CO₂ capture according to the invention.

FIG. 3 is a schematic drawing showing a fossil fuel fired gas turbine cycle power plant with CO₂ capture according to the invention.

FIG. 4 is a schematic drawing showing a fossil fuel fired steam cycle power plant with CO₂ capture according to the invention.

FIG. 5 is a schematic drawing showing a fossil fuel fired combined cycle power plant with CO₂ capture for EOR according to the invention.

FIG. 6 is a schematic drawing showing a fossil fuel fired combined cycle power plant with CO₂ capture, for providing CO₂, N₂ and CO₂ /N₂ mixtures for EOR according to the invention.

FIG. 7 is a schematic drawing showing a fossil fuel fired combined cycle power plant with CO₂ capture for EOR, having a direct contact flue gas cooler according to the invention.

FIG. 8 is a schematic drawing showing a fossil fuel fired combined cycle power plant with CO₂ capture for EOR, having a chilled water direct contact flue gas cooler according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides improved techniques for CO₂ capture from a power plant that is an improvement over the techniques known in the prior art and particularly to CO₂ capture for EOR (Enhanced Oil Recovery) purposes. One goal of the present invention is to create an efficient power plant with CO₂ combustion.

The process according to the present invention is based on a combination of the exhaust gas recirculation process, oxy-fuel process and post combustion process (chemical solvent process). A portion of the exhaust gas from the power plant is recirculated to the air inlet and mixed with both incoming ambient air and an oxygen rich gas stream. The oxygen content of the mixed stream is adjusted by addition of the oxygen rich stream that may be provided from an air separation unit, or other appropriate source. This mixture results in a CO₂ enriched flue gas from the power plant that is partly recycled to the power plant with the remainder flowing to the chemical solvent process unit, where the CO₂ is separated. This process of flue gas recycle and oxygen enrichment are used to control the parameters of the combustion process for the power plant and to make the CO₂ separation easier.

The invention will be described in greater detail with reference to the drawing figures, wherein like components are labeled with like reference numerals. In particular, FIG. 1 is a schematic drawing showing a fossil fuel power plant with CO₂ capture according to the invention. In FIG. 1, a power plant 100 is fueled by a fossil fuel source 10 that may be a solid, liquid or gaseous source, in addition to air from an air source 20, and an oxygen rich gas 32 from an air separation unit (ASU) 30 that is supplied by an air source 34. The oxygen rich gas 32 is preferably 50% to 100% oxygen. The ASU separates the air supplying the oxygen rich gas 32 to the power plant 100 and releasing a waste stream of nitrogen enriched gas 36. The power plant 100 emits flue gas 42 that is treated in a flue gas treatment unit 40. The flue gas treatment unit 40 operates to cool the flue gas 42 and to remove water 44 and various waste 46 while emitting a CO₂ enriched gas stream 48. Part of the CO₂ enriched gas stream 48 is recycled and mixed with the air from the air source 20 and the oxygen rich gas 32 prior to being fed to the power plant 100. An optional process of heating part of the flue gas 42 in a heater 43 and then mixing the pre-heated gas with the recycled portion of CO₂ enriched gas stream 48 can be employed. This allows for pre-heating of the feed gas to the power plant 100. The CO₂ enriched gas stream 48 that is not recycled to the power plant 100 is processed for waste removal in a chemical solvent process unit 50 that emits a waste stream 52 and a CO₂ containing gas 54. The CO₂ containing gas 54 can then be compressed and dried and sent to storage units 60 from which it can be supplied for end user processes 70.

FIG. 2 is a schematic drawing showing a fossil fuel fired combined cycle power plant with CO₂ capture according to the invention. The system shown in FIG. 2 is the same as that shown in FIG. 1 with the exception that the power plant 100 has been replace with a combined gas turbine and steam generator plant. In particular, the mixed CO₂ air and oxygen rich gas is delivered to a gas turbine 200 with the flue gas 42 passing through a heat recovery steam generator with rankine cycle 205 prior to the delivery to the flue gas treatment unit 40. The heat recovery steam generator can optionally be supplied with fossil fuel from the fossil fuel source 10. Further, optionally the recycle CO₂ stream can be fed directly to the plant 200 without premixing with air or oxygen enriched gas.

FIG. 3 is a schematic drawing showing a fossil fuel fired gas turbine cycle power plant with CO₂ capture according to the invention. The system shown in FIG. 3 is the same as that shown in FIG. 1 with the exception that the power plant 100 is more specifically identified as a gas turbine. In particular, the mixed CO₂ air and oxygen rich gas is delivered to a gas turbine 300 with the flue gas 42 delivered to the flue gas treatment unit 40.

FIG. 4 is a schematic drawing showing a fossil fuel fired steam cycle power plant with CO₂ capture according to the invention. The system shown in FIG. 4 is the same as that shown in FIG. 1 with the exception that the power plant 100 is more specifically identified as a steam turbine. In particular, the mixed CO₂ air and oxygen rich gas is delivered to a steam turbine 400 with the flue gas 42 delivered to the flue gas treatment unit 40.

FIG. 5 is a schematic drawing showing a fossil fuel fired combined cycle power plant with CO₂ capture for EOR according to the invention. The system shown in FIG. 5 is the same as that shown in FIG. 2 with the exception that the end user is specifically identified as an EOR. In particular, CO₂ 62 can be delivered from storage unit 60 to an EOR user 72. Alternatively, the nitrogen rich gas 36 from the ASU 30 can be delivered to and EOR user 74. In a further alternative, CO₂ 62 from the storage unit 60 can be mixed with the nitrogen rich gas 36 from the ASU 30 and delivered as a mixture to an EOR user 76.

FIG. 6 is a schematic drawing showing a fossil fuel fired combined cycle power plant with CO₂ capture, for providing CO₂, N₂ and CO₂/N₂ mixtures for EOR according to the invention. The system shown in FIG. 6 is the same as that shown in FIG. 5 with the exception that the CO₂/N₂ gas mixture is derived in a different manner. In particular, part of the recycle CO₂ stream can be treated in oxygen removal unit 600 to remove oxygen and provide a N₂ enriched stream 602 that is then mixed with the CO₂ containing gas 54 to form a CO₂/N₂ gas mixture that is delivered to storage unit 60 and delivery to EOR user 76. The oxygen removal unit 600 can be any suitable unit, such as a catalytic de-oxo unit with CH₄ or H₂ from an external source or from reforming of natural gas, or a conventional burner with CH₄ or H₂.

FIG. 7 is a schematic drawing showing a fossil fuel fired combined cycle power plant with CO₂ capture for EOR, having a direct contact flue gas cooler according to the invention. The system shown in FIG. 7 is the same as that shown in FIG. 5 with the exception that the flue gas treatment unit has been replaced with a more specific water coolant treatment unit and the chemical solvent process has been more specifically identified as an amine wash plant. In particular, the flue gas 42 is treated in water coolant treatment unit 700 to remove water 44 and waste 46 prior to being recycled or further treated in amine wash plant 750. In this system the ASU 30 can be a cryogenic ASU.

FIG. 8 is a schematic drawing showing a fossil fuel fired combined cycle power plant with CO₂ capture for EOR, having a chilled water direct contact flue gas cooler according to the invention. The system shown in FIG. 8 is the same as that shown in FIG. 7 with the exception that the water coolant treatment unit is specifically identified as a chilled water direct contact flue gas cooler. In particular, the flue gas 42 is treated in chilled water direct contact flue gas cooler 800 to remove water 44 and waste 46 prior to being recycled or further treated in amine wash plant 750. This system may also employ a cryogenic ASU.

The invention offers several advantages. By using oxygen enriched air from an ASU as part of the recycle feed to the power plant, the CO₂ concentration in the recycle gas is greater than a feed stream because there is less nitrogen in the feed. This makes the power plant more efficient. In addition, since less nitrogen is entering the system, there is a greater concentration of CO₂ in the flue gas. This makes the chemical solvent treatment process more efficient and increases the efficiency of the whole power plant system. In addition, only a fraction of the air required needs to be separated in the air separation unit when operating according to the invention. Therefore the irreversibility caused by the air separation is reduced. The air separation plant can be more compact in the invention because of the reduced air flow requirement and the size of the absorption plant is also reduced because of the lower nitrogen concentration in the flue gas. It is therefore possible for the system of the invention to be used in either a single-train- or double-train solution, which allows for simpler control methodology.

By using the invention, the mixed gas provided to the power plant is oxygen enriched and therefore the output, efficiency, stability and operation of the power plant is enhanced. Further, the system of the invention can advantageously be used for retrofitting of existing power plants, because only minor changes are required to the power plant input.

It is anticipated that other embodiments and variations of the present invention will become readily apparent to the skilled artisan in the light of the foregoing description, and it is intended that such embodiments and variations likewise be included within the scope of the invention as set out in the appended claims. 

What is claimed:
 1. A power plant system comprising: a fossil fueled power plant having an inlet and an exhaust; a flue gas treatment unit communicating with the exhaust of the power plant; a recycle line communicating with the flue gas treatment unit and the inlet of the power plant; an air separation unit communicating with the inlet of the power plant; an ambient air source communicating with the inlet of the power plant; wherein at least a portion of a CO₂ enriched gas stream from the flue gas treatment unit is mixed with oxygen enriched gas from the air separation unit and ambient air from the ambient air source to form a mixed gas stream that is delivered by the recycle line to the inlet of the power plant.
 2. The power plant system of claim 1 wherein the power plant is a power plant for an enhanced oil recovery system.
 3. The power plant system of claim 1 wherein the power plant is a gas turbine, a steam generator or a combined gas turbine and steam generator.
 4. The power plant system of claim 1 wherein the air separation unit is a cryogenic air separation unit.
 5. The power plant system of claim 1 further comprising a heater communicating with the flue gas treatment unit and with the recycle line, for preheating the CO₂ enriched gas stream.
 6. The power plant system of claim 1 further comprising a chemical processing unit communicating with the flue gas treatment unit wherein the portion of the CO₂ enriched gas stream that is not recycled is treated in the chemical processing unit.
 7. The power plant system of claim 6 wherein the chemical processing unit is an amine wash unit.
 8. The power plant system of claim 1 wherein the flue gas treatment unit is a direct contact flue gas cooler or a chilled water direct contact flue gas cooler.
 9. The power plant system of claim 1 wherein the portion of the CO₂ enriched gas stream that is not recycled is provided to end users.
 10. The power plant system of claim 9 wherein the end user is an enhanced oil recovery operation.
 11. The power plant system of claim 1 wherein the air separation unit produces a nitrogen enriched gas stream that may be provided directly to an end user.
 12. The power plant system of claim 11 further comprising a mixing unit communicating with the flue gas treatment unit and with the air separation unit wherein the portion of the CO₂ enriched gas stream that is not recycled and the nitrogen enriched gas stream from the air separation unit are mixed for supply to end users.
 13. A method of enhancing the operation of a power plant comprising: collecting flue gas from the power plant; recycling at least a portion of the collected flue gas to the power plant; mixing the recycled flue gas with air and oxygen enriched gas; and delivering the mixed gases to the power plant.
 14. The method of claim 13 further comprising supplying the oxygen enriched gas from an air separation unit.
 15. The method of claim 13 wherein the oxygen enriched gas is from 50% to 100% oxygen.
 16. The method of claim 13 further comprising treating the flue gas prior to the step of recycling a portion of the flue gas.
 17. The method of claim 16 wherein treating the flue gas comprises processing the flue gas through a direct contact flue gas cooler or through a chilled water direct contact flue gas cooler.
 18. The method of claim 13 further comprising delivering the portion of the flue gas that is not recycled to an end user.
 19. The method of claim 18 wherein the end user is an enhanced oil recovery operation.
 20. The method of claim 13 further comprising producing a nitrogen enriched gas stream from the air separation unit; and delivering the nitrogen enriched gas stream to an end user.
 21. The method of claim 20 further comprising mixing the portion of the flue gas that is not recycled with the nitrogen enriched gas stream; and delivering the mixture to an end user.
 22. The method of claim 21 further comprising removing oxygen from the flue gas prior to mixing with the nitrogen enriched gas stream.
 23. A method of enhancing the operation of a power plant comprising: collecting flue gas from the power plant; recycling at least a portion of the collected flue gas to the power plant; and delivering air and oxygen enriched gas to the power plant. 